Diameter of particles

An exactly similar expression is obtained for spherical particles, where L and A now refer to the diameters of particles rather than their edge length. 

Cut diameter, diameter of particles of which 50% of those present are collected m ft im... 

When the size of a particle approaches the same order of magnitude as the mean free path of the gas molecules, the setthng velocity is greater than predicted by Stokes law because of molecular shp. The slip-flow correc tion is appreciable for particles smaller than 1 [Lm and is allowed for by the Cunningham correc tion for Stokes law (Lapple, op. cit. Licht, op. cit.). The Cunningham correction is apphed in calculations of the aerodynamic diameters of particles that are in the appropriate size range. 

For determination of the aerodynamic diameters of particles, the most commonly apphcable methods for particle-size analysis are those based on inertia aerosol centrifuges, cyclones, and inertial impactors (Lundgren et al.. Aerosol Measurement, University of Florida, Gainesville, 1979 and Liu, Fine Paiiicles—Aerosol Generation, Measurement, Sampling, and Analysis, Academic, New York, 1976). Impactors are the most commonly used. Nevertheless, impactor measurements are subject to numerous errors [Rao and Whitby, Am. Ind. Hyg. A.s.soc.]., 38, 174 (1977) Marple and WiUeke, "Inertial Impactors, in Lundgren et al.. Aerosol Measurement and Fuchs, "Aerosol Impactors, in Shaw, Fundamentals of Aerosol Sci-... 

The measured diameters of particles shoiild as nearly as possible represent the effective particle size of a dust as it exists in the gas stream. When significant flocculation exists, it is sometimes possible to use measurement methods based on gravity settling. 

Re = R nolds number, dpS UolV Sc = Schmidt number, V/D D = axial dispersion coefficient dp = Diameter of particle or empty tube = Fraction voids in packed bed Uq = Superficial velocity in the vessel. 

Diameter for light phase, ft Diameter of particle, ft or equivalent diameter of spherical particle, ft Minimum diameter of particle that is completely collected, ft Diameter of particle, in. or mm Droplet diameter, ft... 

Modification of filler s surface by active media leads to the same strong variation in viscosity. We can point out as an example the results of work [8], in which the values of the viscosity of dispersions of CaC03 in polystyrene melt were compared. For q> = 0.3 and the diameter of particles equal to 0.07 nm a treatment of the filler s surface by stearic acid caused a decrease in viscosity in the region of low shear rates as compared to the viscosity of nontreated particles more than by ten times. This very strong result, however, should not possibly be understood only from the point of view of viscometric measurements. The point is that, as stated above, a treatment of the filler particles affects its ability to netformation. Therefore for one and the same conditions of measuring viscosity, the dispersions being compared are not in equivalent positions with respect to yield stress. Thus, their viscosities become different. 

C =0verall Drag Coefficient,Dimensionless Dp = Diameter of Particle,ft. 

Dp-min = Minimum diameter of particle that is completely collected, ft... 

The contribution of atmospheric dust to surface dust depends on the dust falling to the earth. This occurs either as dry dust fall or wet washout with rain, snow or hail (1-6,8-10). Dry dust fall occurs by s imentation, impaction, interception or diffusion. Sedimentation, the fall under gravity, may be estimated using Stoke s law which relates the density and diameter of particles to their falling velocity. A particle of density 1.0 g cm"3 and diameter around 0.1 pm would fall with a velocity of around 9 x 10" cm s" ... 

Fig. 6. Absorption spectrum of 2 lO"" M CdS at various times of illumination > 490 nm) in the presence of air >) Stabilizer 6 10" M colloidal SiOj (Ludox HS30). Initial mean diameter of particles 3 nm...

Inertial impaction is the method of choice for evaluating particle or droplet size delivery from pharmaceutical aerosol systems. This method lends itself readily to theoretical analysis, ft has been evaluated in general terms [39] and for specific impactors [40]. Inertial impaction employs Stokes law to determine aerodynamic diameter of particles being evaluated. This has the advantage of incorporating shape and density effects into a single term. 

Before carrying out particle sizing on a sample, the microscope s ocular scale must be calibrated. This is normally done with a stage micrometer, which has a linear graduated scale. The micrometer is aligned with the eyepiece ocular to determine the length per ocular scale division. The ocular can then be used to read the diameters of particles on a slide. When sufficient particles are sized, the length-number mean can be calculated ... 

The interesting information is the correlation between first shell coordination numbers from EXAFS and H/M values from chemisorption, shown in Fig. 6.18. The correlation is as expected high dispersions correspond to low coordination numbers. Of course, what we really need is a relationship between particle size and H/M values. The right hand panel of Fig. 6.18 translates the experimentally determined H/M values of the catalysts into the diameter of particles with a half-spherical shape. Similar calibrations can be made for spherical particles or for particles of any other... 

Process parameters of primary importance include roll speed, differential roll speed, roll gap, metal flow rate, metal stream velocity, and melt superheat. The mass median diameter of particles diminishes exponentially as the roll speed increases. It is possible to obtain a smaller mass median diameter when one of the rolls is kept stationary rather than rotating the two rolls at the same speed. Metal flow rate seems to have a negligible effect on the mass median diameter. However, the mass median diameter increases with increasing metal stream velocity, suggesting that the relative velocity of the metal stream to the periphery of the rolls may be a fundamental variable controlling the mass median diameter. The size distribution is approximately constant for the conditions studied. 

Some other correlations that have been specifically developed for liquid metals include those proposed by Nichiporenko)488 Schmitt)489 Thompson)491 and Date et al)494] Nichiporenkol488 correlated the diameter of particles (powder) of predominant fraction, D h with the arithmetic mean particle diameter (linear average diameter), Z)10, and the Reynolds number as well as the Weber... 

Z-4A), and zeolite H-ZSM-5. The interlayer distance varied by the intercalation was determined from X-ray diffraction patterns. The interlayer space of the crystalline zeolite is separated by the three-dimensional cage structures. The mean diameters of particles were approximately 1 ym. Such small particles formed very stable suspensions with no sign of sedimentation over the time course of the kinetic measurements. The analytical techniques used to obtain the equilibrium concentration are described elsewhere (10-22). All samples were equilibrated for 24-72 h after preparation. The temperature was controlled at 25 °C. 

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